My explanation is as follows: the original image uses a checkerboard pattern. When you make a thumbnail it removes some rows and columns to make the image smaller. When you remove all even rows and columns of a checkerboard the fields that are left are of the same color. Similarly when you remove odd rows and columns.
In this case black and white fields of a checkerboard correspond to pear and apple pixels, so you are left with one of the images.
On my tablet I love it, I have a ThinkPad Tablet 2 and from my extensive tablet usage(starting with an HP TC1100 running XP, iPad and various Android tablets) I think it is by far the best tablet OS to get work done on, from their being no hassle to connect to printers, full USB peripheral support, compatibility with old x86 apps, quick gestures, and the metro/desktop multitasking is great. Plus I think IE10 is the best tablet web browser I've ever used, I wouldn't touch IE on the desktop, Firefox with all my extensions is my only home.
On my desktop I initially would use the metro stuff here and there but after few a few months the novelty has worn off and I very rarely venture into the metro stuff. When used that way Windows 8 is just Windows 7+. I think one of the greatest things about Windows 8, is the promise of Windows Blue, Microsoft's commitment to pushing out major upgrades.
In summary, on a tablet Windows 8 is excellent, on a desktop it's at times between ok to pretty good.
As someone who has been using windows 8 for a few months now, if you are a person who rarely used the start menu to open programs before, windows 8 can easily be used as an improved version of windows 7. Dual monitors also help a lot to make sure you never feel like you are trapped in metro. (Metro only ever shows on one screen)
In this case black and white fields of a checkerboard correspond to pear and apple pixels, so you are left with one of the images.